In general, steel plate products are known as a representative steel product manufactured in steel mills. Such steel plates may be shipped and sold without a separate post-treatment after being manufactured. Operations for improving the quality of products using various post-treatment processes may be performed.
Plating processes for plating a steel plate to prevent a surface thereof from being corroded are a representative post-treatment process.
In plating processes, steel plates may be immersed in a molten plating solution, and the molten plating solution present on the steel plates may be passed through an air knife discharging high-pressure air, thereby controlling a coating weight of the molten plating solution present on the surfaces of the steel plates.
However, in the process in which the steel plates are passed through the air knife, the steel plates may be transformed by being bent in a width direction thereof. Thus, there may be differences in coating weights on steel plates.
Accordingly, in the related art, Korean Patent Application No. 10-2000-0080042 discloses a technique of a nozzle gap control device of an air knife and a method thereof. In the technique, in order to remove the effect of bending of steel plates in the width direction thereof, a gap of the air knife may be adjusted so as to allow the supply of air to be different in a width direction of the air knife.
In the related art, in order to adjust the gap of the air knife, a gap profile control device, including a plurality of air knife nozzle lip gap controllers using an electric motor and a ball screw device, have been used.
However, in the related art, driving devices controlling nozzle lips of an air knife are excessively large, displacement devices provided to transform nozzle lips interrupt operations thereof, and maintenance of the device is not easy, so that the use thereof is inconvenient. Thus, air knives, having been improved to adjust an amount of air discharged thereby, according to bending of steel plates in a width direction, are required.